Effects of long-term tillage regimes on the vertical distribution of soil iron/aluminum oxides and carbon decomposition in rice paddies

Abstract Tillage regimes play an important role in soil organic carbon (SOC) accumulation and atmospheric carbon mitigation. However, the mechanism of SOC decomposition induced by tillage regimes is not clearly understood, particularly related to SOC protection by soil iron (Fe) and aluminum (Al) oxides. Therefore, we assessed three types of soil Fe/Al oxides (Non-crystalline oxides, Feo/Alo; organic bound oxides, Fep/Alp; total free Fe/Al, Fed/Ald), and their relationship with SOC mineralization at the 0–50 cm soil depth after long-term tillage practices in a double rice cropping system in southern China. Four tillage practices were investigated: conservation tillage (no tillage + rice residue mulch, NTS), traditional tillage including rotary tillage (RTS), and plow tillage with or without rice residue incorporation (CTS and CT, respectively). The Feo and Fep/Alp had lower concentrations in deeper soil layers compared with the topsoil. At the 0–50 cm soil depth, the Feo content in the NTS treatment was 1.55 mg g−1, which was 7.5%, 9.3%, and 14.3% higher than that under RTS, CTS, and CT (P